Added notes about MBTiles to front page
Added notes about MBTiles to front page

mapzen/TileStache,SEL-Columbia/TileStache,TileStache/TileStache,Kosta-Github/TileStache,mojodna/TileStache,jbants/TileStache,moskvax/TileStache,TileStache/TileStache,Blechhirn/TileStache,mpuig/TileStache,MetGIS/TileStache,mojodna/TileStache,Billups/TileStache,robpvn/Vector-Tile-Research,jbants/TileStache,moskvax/TileStache,mpuig/TileStache,jbants/TileStache,Billups/TileStache,Kosta-Github/TileStache,Billups/TileStache,MetGIS/TileStache,Blechhirn/TileStache,moskvax/TileStache,mapzen/TileStache,TileStache/TileStache,SEL-Columbia/TileStache,mapzen/TileStache,SEL-Columbia/TileStache,robpvn/Vector-Tile-Research,Kosta-Github/TileStache,robpvn/Vector-Tile-Research,Blechhirn/TileStache,MetGIS/TileStache